The utility of silanes, especially alkylalkoxysilanes, as masonry water repellents is widely known. Compositions currently in use employ solutions of silanes in various organic solvents such as alcohols, see e.g. Seiler, U.S. Pat. No. 3,772,065 and Brown et al, U.S. Pat. No. 4,342,796; or hydrocarbons, see e.g. Linn, U.S. Pat. No. 4,525,213. Principle limitations of such solvent type compositions include the toxicity and the flammability of the solvents employed.
Aqueous silane compositions which are non-toxic and non-flammable have become important as effective masonry water repellent compositions, see Puhringer, U.S. Pat. No. 4,433,013., Schmidt, U.S. Pat. No. 4,517,375; and DePasquale et al., U.S. Pat. No. 4,648,904. Such compositions can have an important drawback, namely that the pH may tend to drift, which causes the silane to react with water and polymerize. This reduces their efficacy by reducing the content of active, water repellent ingredient. To address this problem, buffered silane emulsions were disclosed in commonly assigned U.S. patent application of Wilson, Ser. No. 07/189,146, filed May 2, 1988, and now allowed.
These emulsified compositions also suffer from the need to determine the optimum HLB value (hydrophilic lipophilic balance) for the particular silane to be emulsified and then the appropriate surfactants must be selected. Determination of the HLB and the selection of the appropriate surfactant can be a tedious job of trial and error. However, this knowledge is necessary in order to formulate a stable emulsion. Further, even after careful selection of the surfactant system, homogenization is usually required to keep the oil (silane) phase from separating out. Once an emulsion of this type has separated out due to freeze/thaw instability or other thermal cycling it is not easy to redistribute the oil in the internal phase without vigorous mechanical agitation. A further drawback to the current silane emulsions is the lack of any water bead when the product is initially applied to the concrete surface. This is due to the wetting effect of the residual surfactant left on the surface. There thus remains a need in the art to provide a water based composition which retains stability over a wide range of thermal cycling, does not require time consuming determination of a stable surfactant system and which allows for the addition of particulates, such as water beading additives, without having them precipitate out of the emulsion.
It has now been surprisingly discovered that the use of a neutralized copolymer of an acrylic acid and a long chain alkylmethacrylate as a water thickening agent satisifies this long felt need in the art. The copolymer is believed to be amphipathic so that it is strongly absorbed at the oil/water phase interface and as such also functions as a primary emulsifier. At the same time, it is believed that the polymer forms a three dimensional microgel structure that functions to suspend dispersed particles and the oil droplets of the emulsion. These compositions are quite different from the compositions of the prior art. The use of the water thickening agent makes the determination of the optimum HLB value at which the silane can be emulsified unnecessary. This water thickening agent will work equally well for most water insoluble silanes. The emulsification process does not require homogenization to form a stable emulsion and the use of this copolymer eliminates the need for other surfactants. It is also believed that the thixotropic properties provided by the copolymer allow for the dispersion of solid particulates, such as water beading additives. This allows for the desired effect of visual water repellency. Furthermore, the emulsions thus formed are stable under conditions of widely fluctuating temperatures such as freeze/thaw cycles and elevated storage temperatures.